Field of the Invention
The present invention relates to an image sensing apparatus which senses the image formed by the fluorescence or phosphorescence generated by excitation light.
Description of the Related Art
Japanese Patent Laid-Open No. 2000-292353 discloses a fluorescence image forming apparatus which includes a plurality of light sources to illuminate an image carrier with excitation light which excites a fluorescent material and light which does not excite the material. This apparatus prevents the superimposition of excitation light as noise on a fluorescence image by arranging an excitation light cut filter which cuts off excitation light in front of a CCD camera.
In general, however, the excitation spectrum and fluorescence spectrum of a fluorescent material respectively have corresponding widths. When the peak wavelength difference (wavelength difference caused by a Stokes shift) between the excitation spectrum and fluorescence spectrum is small, unnecessary excitation wavelengths cannot be often sufficiently removed and are left as background noise even by using an optical filter having steep cutoff wavelength characteristics. In the apparatus disclosed in Japanese Patent Laid-Open No. 2000-292353, when the wavelength band of excitation light and the wavelength band of fluorescence have an overlapping range, an excitation light component becomes noise.
In medical and biological applications, it is increasingly the case that near-infrared light with high transmittances is used both as excitation light and fluorescence, that is, excitation light and fluorescence with near wavelengths are used. For this reason, it is difficult to separate excitation light and fluorescence by using an optical filter. In addition, a mechanism for attaching/detaching an optical filter is required when performance of both imaging by using the optical filter and imaging without using the optical filter is required.